The present invention relates generally to a method of separating printed circuit wiring boards and, more particularly, to a method of cyrogenically separating multi-layer printed circuit wiring boards without damaging the printed circuit on the individual layers.
The state of the art of printed circuit wiring board separation is well represented and alleviated to some degree by the prior art apparatus and approaches which are contained in the following U.S. Patents:
U.S. Pat. No. 4,623,255 issued to Suszko on Nov. 18, 1986; and
U.S. Pat. No. 4,766,516 issued to Ozdemir et al on Aug. 23, 1988.
The Suszko patent is an example of the multi-layer nature of printed circuit wiring boards. The examination of microstructures of LSI and VLSI devices is facilitated by employing a method in which the device is photographed through a darkfield illumination optical microscope and the resulting negative subjected to inverse processing to form a positive on a photographic film. The film is then developed to form photographic prints or transparencies which clearly illustrate the structure of the device. The entire structure of a device may be examined by alternately photographing the device and selectively etching layers of the device in order to expose underlying layers.
The Ozdemir et al patent discusses the method and apparatus for securing integrated circuits from unauthorized copying and use wherein at least one additional circuit element that does not contribute toward the integrated circuit's circuit function, but inhibits proper functioning of the integrated circuit in case of an attempted copying or other unauthorized use. The identity of the additional circuit elements is disguised by the visible appearance of an apparent element but with a physical modification which is not readily visible but causes them to function in a different manner, by providing different ICs with unique control codes, or both. Physical modifications not readily visible to a copyist include very narrow open circuit cuts in metalized connection lines, preferably with a focused ion beam or laser beam; and/or disordering the lattice structure or changing the doping level of a semiconductor region, and/or injecting electrical charge into a semiconductor region, preferably with an electron beam. The additional elements can be formed into a control code subcircuit for the IC, with the code disguised by the us of apparent elements.
Many older printed circuit wiring boards are lacking the necessary data for reproducing large quantities of these boards during surge requirements. In many cases, the companies that produced the boards originally are no longer in business or no longer possess the engineering data to manufacture the printed circuit wiring boards again. The only alternative is to reverse engineer an existing printed circuit wiring board. This usually can be accomplished, however, it generally involves a very large cost expenditure in both time and manpower. Thus, it is quite clear that there exists a critical need to find a fast, cost-effective way to reproduce the needed engineering data to reproduce and manufacture new printed circuit wiring boards.
It is therefore very critical in the reproduction and duplication of older printed circuit wiring boards, particularly boards which are multi-layered, that an accurate specimen or model of an original board be produced. The separation of multi-layered printed circuit wiring boards poses a number of great difficulties in the process of obtaining an accurate model of an out of production board. The process of separating or splitting a multi-layered board may totally destroy the only existing board of a particular type or class. It is therefore quite clear that there is a great need to provide a method of separating multi-layered printed circuit wiring boards accurately and without damage to any of the separated layers.
While the above-cited references are instructive, there still remains a need to provide a method of cryogenically separating/splitting multi-layer printed circuit wiring boards to provide a reproducible model in order to produce an exact replica of the original board. The present invention is intended to satisfy that need